Method for centrally setting data rate in a data transmission facility and a device for centrally setting data rates

ABSTRACT

In the method according to the invention for centrally setting data rate in a data transmission facility, the data rate is detected and set at the subscribers on the basis of the data rate setting telegrams sent by the central station. In addition to the interface to the peripheral application, the subscribers include a protocol core and the devices according to the invention for data rate detection and setting. Date rate detection is solved with a telegram detection system wherein one data rate detector is provided for each data rate and the transmitted telegrams in the timed data rate setting phase have the same content for each of the data rates concerned.

[0001] The invention relates to a method for centrally setting data rate in a data transmission facility in accordance with the preamble to claim 1, and to the associated device for centrally setting data rates in accordance with the preamble to claim 10 in a data transmission facility.

STATE OF THE ART

[0002] In a known data transmission facility described in DE 299 08 608 U1, the data rate for transmission of data is set using special telegrams. In this case, all receivers are preset to a data rate in the data rate setting step and are thus ready to receive and evaluate special telegrams. The data rate for future data transmission is set with reference to the special telegram for data rate setting. The content of the special telegram includes the information regarding the data rate. This is always transmitted with a single, preset data rate for the purpose of setting the data rate. However, the setting of the data rate according to this described method has the critical disadvantage that for central data rate setting the central station must send out special telegrams. This data transmission facility does not permit compatibility with subscribers that have no data rate setting, since transmission is only assured if all subscribers are capable of evaluating the special telegram.

[0003] From DE 44 18 622 C2, a method is known for determining the transmission rate in a bus system, according to which the transmission rate corresponding to the bit length is selected from a table by bit length measurement. In this described method, a counter is started when bit edge detection is begun, and stopped again after the following bit edge. The counter value determined thereby represents a bit length that corresponds to a data rate. The counter value is compared with a standard table of reference bit lengths. If the measured bit length matches a value in the table, the data rate is set accordingly. The method presented here is highly unreliable for data transmission facilities because signal edges in data circuits may be created by, for example, electromagnetic interference. As a consequence, reliable data rate setting in an industrial environment where electromagnetic disturbances abound is not possible with this measurement method. Since the counter for bit length measurement returns a value that corresponds to a data rate even with predetermined deviations, the realisation thereof involves a great deal of effort and must be clocked at a higher system speed. Otherwise the measurement will become very inaccurate at higher data rates because of the system-conditioned sampling error.

[0004] In INTERBUS basics and practise, ISBN 3-7785-2471, 1998, a serial data transmission protocol according to the INTERBUS transmission method is described. Synchronisation of the telegrams and the function of the status telegrams are described here. This description always assumes a fixed data rate, which must be preset on all subscribers. In the data transmission method described here, no provision is made to enable the data rate to be set or changed centrally for all subscribers.

OBJECT OF THE INVENTION

[0005] The object of the invention is to provide a data transmission facility that allows a data rate determined by the central station to be set at the subscribers. To keep the data rate setting phase as brief as possible for the entire data transmission facility, it is necessary to provide an early forwarding system for the data rate setting telegrams from one subscriber to the next subscriber in the direction of the data flow. In existing data transmission facilities, in which the data rate cannot be set centrally, subscribers must be capable of being coupled and operated with a variable data rate, the subscribers being capable of setting themselves automatically to the fixed data rate.

SOLUTION TO THE OBJECT

[0006] The object is solved according to the invention by the features described in claim 1 and the device suggested according to claim 10.

[0007] In the method according to the invention, the data rate is set at the coupled subscribers in a transmission facility before the beginning of transmission, starting from a central station. The transmission facility consists of a central station, which transmits output data to the subscribers connected to the bus, and in the other direction receives input data from the subscribers. Besides an interface to the peripheral application, the subscribers contain a protocol core and devices for data rate determination and data rate setting. In the method according to the invention, data rate detection is solved with a means for telegram detection, such that one data rate detector is provided to detect each data rate. The means for telegram detection is provided in each data rate detector, and telegram detection is triggered not by a certain bit sequence, but by a significant pattern. This pattern may represent multiple telegram types. In the present method, telegrams are regenerated to stabilise the bit length during data rate setting in each of the data rate detectors. For example, in a data transmission facility according to the INTERBUS protocol, status telegrams are identified on the basis of significant bits in the telegram and the pause lasting several bit lengths between two status telegrams. In the method according to the invention, the data rate may be reliably determined after a single status telegram and the associated pause have been detected. The particular advantage of the present invention consists in that an existing protocol, such as that of the INTERBUS, does not need to be changed. The current telegram patterns and timed sequences at the start of the data transmission can also be used for setting the data rate. In this event, it is possible to use those status telegrams that have already been used to cancel the reset, as described in INTERBUS basics and practise, ISBN 3-7785-2471 1998, in the setting of the data rate. It is not necessary to change the protocol or to define a new data rate telegram.

[0008] The invention will be described in the following with reference to an exemplary embodiment and the associated figures.

HEADINGS OF FIGURES

[0009]FIG. 1: shows an exemplary arrangement of the central station and the subscribers connected to the bus in the application according to the invention.

[0010]FIG. 2: is a schematic representation of the device with the individual blocks in a subscriber that are necessary for operating the bus and setting the data rate according to the invention.

[0011]FIG. 3: shows the timed phases at the beginning of data transmission.

[0012]FIG. 4: is a schematic representation in the timing diagram of the signal sequences on the data circuits in the individual timed phases.

[0013]FIG. 5: is a schematic representation in the timing diagram of the signal sequences on the data circuits for the data rate setting phase.

[0014]FIG. 6: is a schematic representation of a variant of a device with the individual blocks in a subscriber that are necessary for operating the bus and setting the data rate according to the invention, wherein the data rate can be firmly preset.

[0015] Key to Parts

[0016]1: Central station, Bus master

[0017]2: Subscriber 1, Bus module 1

[0018]3: Subscriber 2, Bus module 2

[0019]4: Subscriber 3, Bus module 3

[0020]5: Bus circuit, Outward data path segment 1

[0021]6: Bus circuit, Outward data path segment 2

[0022]7: Bus circuit, Outward data path segment 3

[0023]8: Bus circuit, Return data path

[0024]20: Reset signal for the protocol core

[0025]21: Data output of the protocol core

[0026]22: Data input

[0027]23: Data output

[0028]24: Decoder of the programmable data rate

[0029]25: Data rate validity signal BD1

[0030]26: Data rate validity signal BD2

[0031]27: Data rate validity signal BD3

[0032]28: Internal data circuit

[0033]29: Application data

[0034]30: Data rate detection

[0035]31: Protocol core

[0036]32: Data rate detector for data rate BD1

[0037]33: Data rate detector for data rate BD2

[0038]34: Data rate detector for data rate BD3

[0039]35: Data rate controller

[0040]36: Data circuit input selection switch

[0041]37: Data circuit output change-over switch

[0042]38: Application interface

[0043]39: Visual display signal of the set data rate

[0044]41: Phase reset

[0045]42: Data rate setting phase

[0046]43: Switch to protocol core phase

[0047]44: Activate protocol core phase

[0048]45: Bus operation, data transmission phase

[0049]51: Significant bit sequence

[0050]52: Significant pause

[0051]53: Data rate setting telegram

[0052] Exemplary Embodiment

[0053]FIG. 1 shows an exemplary arrangement of a data transmission facility with central station 1 and several subscribers 2, 3, 4 disposed one after the other with the data connection assured by bus circuits 5, 6, 7, 8.

[0054]FIG. 2 shows the essential functional devices within a subscriber 2, which are required in order to detect the data rate of the data rate setting telegrams received at data input 22, and to set the data rate for protocol core 31. For example, data rate detector 32 for data rate BD1 is provided to detect the data rate of 500 bit/s, data rate detector 33 for data rate BD2 for 2 Mbit/s, data rate detector 34 for data rate BD3 for 8 Mbit/s. During data rate setting, all data rate detectors 32, 33, 34 are active simultaneously and receive telegrams via data input 22. When a valid telegram has been detected, the signal validating data rate BD1 25, or BD2 26, or BD3 27, is activated. As a rule, only one data rate detector may detect a single valid data rate, so that consequently only one data rate validity signal may be actively present at the data rate controller 35. As soon as data rate controller 35 has detected an active signal validating a data rate 25, 26 or 27, the controller switches data circuit input-output selection switch 36 to position B. C or D, to select the data rate detector having the detected data rate. In this way, a bypass-type connection is established through subscriber 2 by way of internal data circuit 28 and data circuit output selection switch 37 in position A, so that downstream slave module 3 can also start data rate setting, and so on. In order to set a stable data rate, data rate controller 35 does not fix data rate BD until a specified number of telegrams have been detected or a specified time period has elapsed. In the data rate setting phase, rate controller 35 activates a reset signal 20 to protocol core 31. When the valid data rate has been detected and the data rate detection 30 has been transferred to protocol core 31, reset signal 20 is deactivated and data rate output change-over switch 37 is switched to protocol core data output 21. Then protocol core 31 begins the protocol evaluation and is ready for data transmission. Application interface 38 establishes the link between the external application and the protocol core. This is also where the information regarding the set data rate 39 is made available to application interface 38.

[0055]FIG. 3 is a embodiment of the method according to the invention on the example of the INTERBUS, showing the timed phases for setting the data rate. In the first, “Reset” phase 41, all components are reset to the initial state in response to a protocol-specific pause. In the data rate setting timed phase 42, telegrams are sent out from the central station; the telegrams contain a predetermined number of bits, of which only the significant bits are evaluated for purposes of data rate detection.

[0056] When the data rate setting timed phase 42 has elapsed, “Switch to protocol core” phase 43 follows, in which the internal data circuit is then switched out of the bypass-type routing and back to the protocol core. The protocol core activates at a later point in time 44. After this, data transmission can begin in accordance with the protocol provided. This is data transmission phase 45.

[0057]FIG. 4 shows in chronological representation an example of telegram activity at data input 22 of reset signal 20 for the protocol core and the functional switching position of data circuit output change-over switch 37 during the individually described timed phases. Telegram activity also takes place on the bus circuits of the other segments 6, 7, 8.

[0058]FIG. 5 shows the telegrams as they may be used to set the data rate in a slave module. In the data rate setting timed phase, the central station repeatedly sends data rate setting telegrams 53 to all subscribers over bus circuit 5. A data rate setting telegram consists of a significant bit sequence 51 followed by a specific bit pause 52. Since this sequence of data rate setting telegrams is repeated several times in the same manner, only the data rate detector provided for the corresponding data rate can detect that data rate.

[0059] The other data rate detectors are also active, but since the received data rate setting telegram does not match the timed bit pattern they are expecting, they do not detect a data rate.

[0060]FIG. 6 shows the essential functional devices within a subscriber 2 in an embodiment that allows the data rate to be firmly preset in subscriber 3. Decoder 24 for a firmly settable data rate selects only one data rate detector from the three data rate detectors 32, 33, 34 possible. When the selected data rate, BD1, BD2 or BD3 has been detected, the respectively selected data rate detector transfers the subsequently received data rate setting telegrams through internal data circuit 28 and sets data circuit output change-over switch to data output 23. Data rate controller 35, protocol core 31 and application interface 38 function in the same way, as was explained in the description of FIG. 2. At the same time, the data rate setting must be controlled in such manner by the central station that, starting with the first data rate, the data rate setting phase 42 is repeated until the data rate setting telegrams sent over bus circuit data return path 13 are received and detected. Then the central processor repeats “Reset” phase 41 and “Data rate setting” phase 42, but this time with the previously detected data rate.

[0061] In this way, the data rate for the entire data transmission facility can be set at a single subscriber. 

1. A method for centrally setting data rate in a data transmission facility with a central station (1) and at least one subscriber (3, 4, 5) connected to the field bus, which central station includes a protocol core (31) and one or more devices for setting data rate (32, 33, 34, 35), characterized in that the devices for setting data rate receive and evaluate data rate setting telegrams (53), and when the data rate of the received data rate setting telegram (53) is detected from a plurality of possible data rates, the data rate is set in protocol core (31).
 2. The method according to claim 1, characterized in that data rate setting occurs in a time period reserved for that purpose.
 3. The method according to claims 1 and 2, characterized in that protocol core (31) is deactivated in data rate setting phase (42).
 4. The method according to any of claims 1 to 3, characterized in that in data rate setting phase (42), logic switches (36, 37) inside the subscriber (3, 4, 5) switch internal data circuit (28) so that protocol core (31) is bridged in the manner of a bypass.
 5. The method according to any of claims 1 to 4, characterized in that in data rate setting phase (42), the data rate setting telegrams (53) received at data input (22) in a subscriber (2) are transferred at the data output to the data input (22) of the subsequently configured subscriber (3) in each case.
 6. The method according to any of claims 1 to 5, characterized in that the data rate setting telegrams (53) have respectively the same content for each data rate.
 7. The method according to any of claims 1 to 6, characterized in that a small number of bits having known state are used in order to detect the data rate from data rate setting telegrams (53).
 8. The method according to any of claims 1 to 7, characterized in that the bit sequence of the data rate setting telegrams is used for another function in the data transmission facility.
 9. The method according to any of claims 1 to 8, characterized in that the data rate may be firmly set at one subscriber (2, 3, 4) and central station (1) and all other subscribers are set to this data rate.
 10. A device for centrally setting data rate in a data transmission facility with a central station (1) and at least one subscriber (3, 4, 5) connected to the field bus, which central station includes a protocol core (31) and one or more devices for setting data rate (32, 33, 34, 35), setting data rate, characterized in that one data rate detector (32, 33, 34) is provided for each data rate in every subscriber (3, 4, 5), each detector receiving and evaluating the data rate setting telegrams (53) simultaneously, and when an expected significant bit pattern is detected from a plurality of possible data rates, the data rate is set in protocol core (31).
 11. The device according to claim 10, characterized in that protocol core (31) is deactivated in data rate setting phase (42).
 12. The device according to claim 10 or 11, characterized in that in data rate setting phase (42), internal logic switches (36, 37) transfer received data rate setting telegrams (53) to output (23).
 13. The device according to any of claims 10 to 12, characterized in that in data rate setting phase (42), internal logic switches (36, 37) transfer received data rate setting telegrams (53) to output (23).
 14. The device according to any of claims 10 to 13, characterized in that data rate setting telegrams (53) are used for an additional function in the data transmission facility.
 15. The device according to any of claims 10 to 14, characterized in that in one of subscribers (2, 3, 4) the data rate is firmly fixed by preselection of the data rate detector (32, 33, 34), so that in the data rate setting phase (42) only data rate setting telegrams having the firmly set data rate are forwarded via output (23) to the next subscriber (3, 4). 